An avalanche photodiode (APD) has a Geiger mode in which it is operated with a bias voltage lower than a breakdown voltage and a linear mode in which it is operated with a slightly high bias voltage in the vicinity of the breakdown voltage. The avalanche photodiode in the Geiger mode is also called single photon avalanche diode (SPAD).
The SPAD is a device capable of detecting a single photon on a pixel basis, by a process in which carriers generated by photoelectric conversion are multiplied in a high-electric-field PN junction region provided on a pixel basis.
In PTL 1, there is proposed a technology in which a layer for forming a high-electric-field region is embedded and is depleted by a bias, for the purpose of enhancing sensitivity of SPAD pixels. In PTL 2, there is proposed a technology for realizing a reduction of crosstalk to neighboring pixels due to light emission in a high-electric-field region, by a structure having an isolation between pixels.